Roku headlines a six-stock wave into the S&P MidCap 400, with most changes hitting June 22.
S&P MidCap 400 (^SP400)
Added:
- Coeur Mining (CDE) — June 22
- Roku (ROKU) — June 22
- Sanmina Corp (SANM) — June 22
- Sirius XM (SIRI) — June 11
- Semtech Corporation (SMTC) — June 22
- Viavi Solutions (VIAV) — June 22
Removed:
- Blackbaud (BLKB) — June 22
- Bellring Brands (BRBR) — June 22
- Concentrix (CNXC) — June 22
- Coty (COTY) — June 22
- Flex Ltd (FLEX) — June 22
- Masimo (MASI) — June 11
The mechanical reason these dates matter: index funds tracking the S&P 400 are forced to buy every addition and sell every deletion at roughly the same time. That concentrated, predictable demand tends to push adds higher and drops lower in the days around the effective date — a pattern momentum traders have watched for decades.
Roku's inclusion is the one to watch. It carries far more liquidity and market attention than typical mid-cap additions, which can amplify the buying pressure as trackers scramble to establish positions before the open on June 22.











